1. Field of the Invention
This invention relates to a process for the liquid phase separation of mannose from glucose or from other mixtures containing mannose. More particularly and in a preferred embodiment, this invention relates to such a separation by selective adsorption onto certain types of zeolitic molecular sieves.
2. Description of the Prior Art
The sugar alcohol mannitol is a widely-used, commercially-significant material. It can be used to make resins, plasticizers, detergent builders, dry electrolytic condensers, as well as sweeteners and diluent excipient for drugs. Unfortunately, the current price of mannitol is high and therefore some of these commercial applications are not economically attractive. Mannitol can be made by hydrogenation of invert sugar, which gives a syrup containing about 26% mannitol and a yield of crystalline mannitol of about 17%. The remaining 9% mannitol in the mother liquor is difficult to recover. However, mannitol can also be made by hydrogenation of mannose, the corresponding sugar, with approximately 100% yield. Mannose is thus commercially significant, because it is the most efficient raw material for the manufacture of mannitol. In addition, L-mannose has been identified as one sugar in a series of reactions designed to produce L-sucrose, a possible non-nutritive sweetener (see CHEMTECH, August, 1979, pp. 501 and 511). Furthermore, mannose is useful as a corrosion inhibitor, as a garment softening agent or as a detergent builder. It is therefore obviously commercially desirable to have and there is a need for an inexpensive and efficient source of mannose.
There are presently two major sources of mannose: by epimerization of glucose (see, e.g., U.S. Pat. Nos. 4,029,878, 4,713,514 and 4,083,881) or from hydrolysis of hemicellulose or plant tissue (see, e.g., U.S. Pat. No. 3,677,818). The epimerization reaction yields a mixture of mannose and glucose. The hydrolysis of hemicellulose is sometimes a part of the process in making pulp from wood, or a part of the process to convert plant tissue to sugars. In both cases, the raw material is not a purified hemicellulose mannan, and the product is a mixture of many mono- and di-saccharides.
The products of epimerization of glucose can be hydrogenated directly to give a high mannitol syrup, rather than producing mannitol by separating mannitol from sorbitol. Or, as an alternative, the mannose can be separated from the glucose first, then hydrogenated to make pure mannitol.
It is also known to use a cationic exchange resin (i.e., the calcium form of Rohm and Haas' Amberlite XE200) to separate mannose from glucose (see, e.g., British Pat. No. 1,540,556). However, this method seems to be inefficient. Specifically, the feed (29.0% mannose, 67.1% glucose) is first passed through a 213 cm resin column to enrich the mannose to 87%. The 87% mannose fraction is then passed through a second identical column to give a fraction which contains at most 98% mannose. In practical operation, a process like this would be both cumbersone and expensive and a better adsorbent would appear to be desirable to make the method of separation by adsorption practical.
The problem of recovering mannose from plant tissue hydrolyzate is substantially more difficult than separating mannose from glucose. The sugar mixture contains many different sugars. Besides mannose and glucose, it contains arabinose, galactose, xylose, and cellobiose. One of the possible compositions of sodium-based sulfite liquor (a typical plant tissue hydrolyzate) is:
______________________________________ Sodium Lignosulfonate 61.5% Xylose 3.5% Arabinose 1.5% Mannose 14.2% Glucose 5.5% Galactose 3.8% ______________________________________
The mannose in such a mixture can be recovered by forming mannose bisulfite adducts (see, e.g., U.S. Pat. No. 3,677,818). In such a process, Na.sub.2 S.sub.2 O.sub.5 is added to the sulfite liquor, then the mixture is seeded with sodium mannose bisulfite to promote the crystallization of adducts. The sodium mannose bisulfite is redissolved in water and mannose is regenerated by adding a bicarbonate reagent. After the decomposition reaction is complete, ethanol is added to precipitate out sodium sulfite. After several more steps, this process recovers pure mannose at 85% yield. A process like this is not only expensive, but also yields a huge amount of chemical waste, causing serious disposal problems.
U.S. Pat. No. 3,776,897 teaches methods of separating lignosulfonate from hemicellulose and mono-saccharides. Hemicellulose is first precipitated by adding a proper water-soluble solvent into the mixture. By adding more of the same solvent, lignosulfonate is separated from mono-saccharides. No specific method to recover mannose from the mono-saccharide mixture is disclosed.
Canadian Pat. No. 1,082,698 discloses a process for separating a monosaccharide from an oligosaccharide by selective adsorption onto an X or Y zeolite containing either ammonium or Group IA or IIA metal exchangeable cations. No specific data are given for separating the monosaccharide mannose from other monosaccharides or disaccharides.
Copending, commonly-assigned U.S. patent application Ser. No. 417,577, filed Sept. 13, 1982 (D-13,577), now abandoned, discloses a process for the bulk separation of inositol by selective adsorption on zeolite molecular sieves. Table III of that patent application shows a retention volume for D-mannose and a separation factor for inositol with respect to D-mannose, for a NaX zeolite.
Wentz, et al., in "Analysis of Wood Sugars in Pulp and Paper Industry Samples by HPLC", Journal of Chromatographic Science, Vol. 20, August, 1982, pp. 349-352, disclose a high performance liquid chromatography (HPLC) method for analyzing wood sugars (i.e., glucose, mannose, galactose, arabinose and xylose) in a pulp hydrolyzate or a spent sulfite liquor by selective adsorption onto a polystyrene/divinyl benzene cation exchange resin.
Olst, et al, in Journal of Liquid Chromatography, Vol. 2, No. 1, pp. 111-115 (1979), disclose a HPLC method for the analysis of glucose-fructose-mannose mixtures resulting from the commerical alkali-catalyzed production of High Fructose Syrup from glucose. An unmodified silica is employed as the adsorbent and acetonitrile as the desorbent.